OPERATION AND MAINTENANCE OF VRLA BATTERIES

MAINTENANCE – FREE SECONDARY CELLS (VRLA)

1.0 INTRODUCTION

Maintenance free, valve-regulated lead-acid (VRLA) batteries ensure a reliable, effective and user friendly source of power. It is spill proof, leak proof and explosion resistant and there is no need to add water or to clean terminals. It has low self-discharge rate which eliminates the need for equalizing charges. The container is made of polypropylene. Each plate is individually wrapped by a highly absorbant, microporous glass separate developed specially for VRLA batteries. The chemically inert glass ensures life long service. The absorbed electrolyte ensures that there is no spillage even in the unlikely event of puncture of the cell. Gas evolution under float conditions is negligible. The water loss throughout life due to gassing is roughly 0.1% of the total electrolyte present in the cell. This will in no way affect performance and also eliminate the need for specially ventilated battery room and acid resisting flooring. As the batteries can be installed in stacks, there will be considerable space saving also.

Various capacities of Batteries are 120 AH, 200 AH, 400 AH, 600 AH, 1000 AH, 1500 AH, 2000 AH, 2500 AH, 3000 AH, 4000 AH and 5000 AH.

1.1 VRLA Technology – A brief review of Chemical ReactionThe electrode reactions in all lead acid batteries including VRLA battery are

basically identical. As the battery is discharged, the lead dioxide positive active material and the spongy lead negative active material react with the sulphuric acid electrolyte to form lead sulphate and water. During charge, this process is reversed. The Columbic efficiency of the charging process is less than 100% on reaching final stage of charging or under over charge conditions, the charging energy is consumed for electrolytic decomposition of water and the positive plates generate oxygen gas and the negative plates generate hydrogen gas.

Under typical charging conditions, oxygen at the positive plate occurs before hydrogen evolution at the negative. This feature is utilized in the design of VRLA batteries. In flooded cells, the oxygen gas evolved at the positive plate bubbles upwards through the electrolyte and is released through the vents. In MF-VRLA batteries the oxygen gas evolved, at the positive plate, instead of bubbling upwards is transported in the gas phase through the separator medium to the negative plate. The separator is a highly absorbent glass matrix type with very high porosity, designed to have pore volume in excess of the electrolyte volume (starved electrolyte design), due to which the oxygen gas finds an unimpeded path to the negative plate. Reaction reduces the oxygen gas with

the spongy lead at the negative plate, turning a part of it into a partially discharged condition, thereby effectively suppressing the hydrogen gas evolution at the negative plate. This is what is known as the oxygen recombination principle. The part of negative plate, which was partially discharged, is then reverted to the original spongy lead by subsequent charging. Thus, a negative plate keeps equilibrium between the amount, which turns into spongy lead by charging and the amount of spongy lead, which turns into lead sulphate by absorbing the oxygen gas generated at the positive plate. The oxygen recombination principle can be shown by the following reaction:

1. Reaction at positive plate:

H2O = ½ O2 + 2e– … (1)

2. Reaction at negative plate :

Pb + 1/2O2 = PbO … (2)

PbO+H2SO4 = PbSO4 + H2O … (3)

To reaction (1)

PbSO4 + 2H+ + 2e– = Pb + H2SO4 … (4)

To reaction (3)

To reaction (2)

3. The total reaction at negative plate

½O2 +2H+ = H2O

Thus, the recombination technology makes the battery virtually Maintenance Fee.

1.2 Technical Specification of 1000 AH Battery

1. Capacity of the Battery @ 10 Hr. rate discharge to 1.75 ECV

: 1000 AH

2. Nominal Voltage per cell of fully charged battery at 27oC

: 2.0 V

3. Open Circuit Voltage (OCV) of fully charged battery at 27oC

: 2.15 V

4. Recommended Float Voltage Condition(i) Terminal Voltage of Charger

: 2.25 V/Cell

(ii) Float charging current at 2.25 V/cell

: Maximum current to be limited to 20% of the rated AH

5. Recommended Boost charging condition for quick charging at 27oC

: 2.30 V/Cell

6. Internal resistance of the cell : 0.257 milli ohms7. Life Expectancy of the Battery : 4000 Cycles at 20% Depth of Discharge or 20 years

under Float condition

8. Containers:(i) Material : Polypropylene (Spl. Grade)(ii) Thickness of wall : 2.3 mm (Approx.)

Container and cover -

Polypropylene Co-polymer housed in a steel tray

Separator -

Spun glass microporous matrix

Safety valve -

Explosion proof, pressure-regulating and self-resealing type

Positive plate -

Patented MFX alloy

Negative plate -

Lead Calcium allow

Terminal -

Integral lead terminal with solid copper core

Self discharge -

Less than 0.5% per week

Charging -

Current limited, constant potential

Float charge -

2.25 VPC at 27oC with a max. current limit of 20% of rated capacity in amperes

Boost charge -

2.30 VPC at 27oC with a max. current limit of 20% of rated capacity in amperes

Connectors -

Heavy-duty, lead plated copper connectors

Life expectancy -

Float service at 27oC – upto 20 years

-

Cycle duty at 27oC – 80% DOD – 1200 Cycles

-

Cycle duty at 27oC – 20% DOD – 4000 Cycles

Fig. Power Stack Cell – Cut Section

1.3 Freshening Charge

General Batteries lose some charge during as well as during the period prior to installation. A battery should be installed and given a freshening charge after receipt as soon as possible. Battery positive (+) terminal should be connected to charge positive (+) terminal and battery negative (-) terminal to charger negative (-) terminal.

Constant Voltage MethodConstant voltage is the only charging method recommended. Most modern chargers are

of the constant voltage type.

Determine the maximum voltage that may be applied to the system equipment. This voltage, divided by the number of cells connected in series, will establish the maximum volts per cell (VPC) that may be used.

Table B lists recommended voltages and charge times for the freshening charge. Select the highest voltage the system allows but not exceeding 2.37 volts per cell to perform the freshening charge in the shortest time period. The charging current should be limited to a maximum of 20% of the rated capacity in Amps.

Table – B

Cell Volts Time

2.25 30 hrs

2.30 12 hrs

Note : Time periods listed in Table B are for temperatures from 15oC to 40oC. For temperatures below 15oC double the number of hours.

Raise the voltage to the maximum value not exceeding 2.37 volts per cell permitted by the system equipment. When charging current has tapered and stabilized (no further reduction for three hours), charge for the hours shown in the above table or until the lowest cell voltage ceases to rise. Correct charge time for the temperature at the time of stabilization. To determine lowest cell, monitoring should be performed during the final 10% of the charge time.

1.4 Operation:

GeneralAll POWER STACK batteries are rated to an end cell voltage of 1.75 VPC at all rates of

discharge.

1.4.1 Floating Charge MethodIn this type of operation, the battery is connected in parallel with a constant voltage

charger and the critical load circuits. The charger should be capable of maintaining the required constant voltage at battery terminals and also supply normal connected load where applicable. This sustains the battery in a fully charged condition and also makes it available to resume the emergency power requirements in the event of an AC power interruption or charger failure.

1.4.2 Float and Boost VoltagesGiven below are the float and boost voltage recommended for the POWER STACK

battery system. The average “Volts per cell” (VPC) value of the series string should be set to the recommended voltage under Float and Boost conditions.

RECOMMENDED FLOAT VOLTAGE 2.25 VPC AT 27oCRECOMMENDED BOOST VOLTAGE 2.30 VPC AT 27oC

Modern constant voltage output charging equipment is recommended for the floating charger method of operation of batteries. This type of charger, properly adjusted to the recommended floats voltage and following recommended surveillance procedures, will assist in obtaining consistent serviceability and optimum life. The charging current for the battery should be limited to 20% of its nominal AH capacity. After the battery has been given its freshening charge (refer to section 4), the charger should be adjusted to provide the recommended float voltage at the battery terminals. Do not use float voltage lower or higher than those recommended. This will result in reduced capacity and/or reduced battery life. Check and record battery terminal voltage monthly. See Section 8, RECORDS Item B. If normal battery float voltage is above or below the recommended value adjust charger to provide proper voltage as measured at the battery terminals.

Voltmeter Calibration Panel and portable voltmeters used to indicate battery voltage should be accurate at the

operating voltage value. The same holds true for portable meters used to read individual cell voltages. These meters should be checked against a standard every six months and calibrated when necessary.

RechargeAll batteries should be recharged as soon as possible following a discharge with constant

voltage chargers.

Determining State-of-ChargeThe approximate state of charge of the battery, to some extent can be determined by the

amount of charging current going to the battery. While charging the current shown by the charger ammeter will start to decrease and will finally stabilize when the battery becomes fully charged, if the normal connected load is constant (no emergency load connected). The state when the current level remains constant, after it has started decreasing, for three consecutive hours would indicate full state of charge condition and the battery will be ready for normal use.

If the normal connected load is variable (e.g. Telecom application) the state when the voltage across the battery terminals is stable for six consecutive hours would indicate full state of charge condition and the battery is ready for normal use.

Temperature of the CellThe temperature of the POWER STACK cells cannot be measured during operation.

However, cell temperatures are normally within +5oC of the ambient. All performance characteristics are measured at ambient temperature and corrected to 27oC.

1.5- Equalizing Charge

GeneralUnder normal operating conditions an equalizing charge is not required. An equalizing

charge is a special charge given to a battery when non-uniformity in voltage has developed between cells. It is given to restore all cells to a fully charged condition. Use a charging voltage higher than the normal float voltage and for a specified number of hours, as determined by the voltage used.

Non-uniformity of cells may result from low float voltage due to improper adjustment of the charger or a panel voltmeter, which reads an incorrect (higher) output voltage. Also, variations in cell temperatures greater than 3oC in the string at a given time due to environmental conditions or module arrangement can cause low cells.

Equalizing FrequencyAn equalizing charge should be given when the following conditions exist.

(A) The float voltage of the pilot cell (as per section 7) is atleast 0.05V blow the average float voltage per cell in the blank.

(B) A recharge of battery is required in a minimum time period following an emergency discharge.

(C) Accurate periodic records (see section 8) of individual cell voltages show an increase in spread since the previous readings.

Equalizing Charge MethodConstant Voltage charging is the method for giving an equalizing charge. Determine the

maximum voltage that may be applied to the system. This voltage, divided by the number of cells connected in series, will establish the maximum volts per cell that may be used to perform the equalizing charge in the shortest period of time. Refer to Table-C for voltage and recommended time periods.

Table-CCell Volts Time

2.25 30 hrs2.30 12 hrs

Note : Time periods listed in Table C are for ambient temperatures from 15oC to 40oC. For temperatures less than 15oC double the number of hours.

Raise the voltage to the maximum value permitted by the system equipment or recommended equalizing charge voltage whichever is lower. When charging current has tapered and stabilized (no further reduction for three hours). Continue charging for the hours shown in

Table C until the lowest cell voltage ceases to rise. Monitoring of cell voltages should be started during the final 10% of the applicable time period to determine lowest cell voltage in the battery system.

1.6 – Pilot CellA pilot cell is selected in the series string to reflect the general condition of all cells in the

battery. The cell selected should be the lowest cell voltage in the series string following the initial charge. See section 4 FRESHENING CHARGE. Reading and recording pilot cell voltage monthly serves as an indicator of battery condition between scheduled overall individual cell readings.

1.7 – RecordsA complete recorded history of the battery operation is most desirable and helpful in

obtaining satisfactory performance. Good records will also show when corrective action may be required to eliminate possible charging, maintenance or environmental problems.

The following surveillance data must be read and permanently recorded for review by supervisory personnel so that any necessary remedial action is taken.

(A) Upon completion of the freshening charge and with the battery on float charge at the proper voltage for one week, read and record the following :

(1) Individual cell voltage(2) Battery terminal voltage(3) Ambient temperature

(B) Every 3 months, a complete set of readings as specified in paragraph A above must be recorded.

(C) Whenever the battery is given an equalizing charge, an additional set of readings should be taken and recorded as specified in paragraph A above.

The suggested frequency of record taking is the absolute minimum to protect warranty. For system protection and to suit local conditions or requirements, more frequent readings may be desirable.

1.8 – Temporary Non-useAs installed battery that is expected to stand idle for over 6 months should be treated as

follows. Give the battery an equalizing charge as per section 6. Following the equalizing charge, open connections at the battery terminals to remove charge and load from the battery .Every six months, temporarily connect battery to charger and give it an equalizing charge. To return the battery to normal service, re-connect the battery to the charger and load, give an equalizing charge and return the battery to float operation.

1.9 – Unit CleaningPeriodically clean cell covers with a dry 55 mm paintbrush to remove accumulated dust.

If any cell parts appear to be damp with electrolyte or show signs of corrosion, contact your local representative of the manufacturer.

CAUTION

Do not clean plastic parts with solvents, detergents, oils, mineral spirits or spray-type cleaners as these may cause crazing or cracking of the plastic materials.

1.10 – Checking ConnectionsBattery terminals and intercell connections should be corrosion free and tight for trouble

free operation. Periodically these connections should be inspected.

If corrosion is present, disconnect the connector from the terminal.

Gently clean the affected area using a brush or scouring pad. Apply a thin coating of petroleum jelly to the cleaned contact surfaces, reinstall connectors and retorque connections.

ALL TERMINALS AND INTERCELL CONNECTIONS SHOULD BE RETORQUED ATLEAST ONCE EVERY YEAR.

1.11– Determination of State of Charge of VRLA BatteriesSealed Maintenance Free Valve Regulated Lead Acid Batteries represent the state of the

art in Lead Acid technology. The maintenance-free feature of these batteries often raises a practical problem in the field. How can the battery bank be monitored? In conventional flooded batteries, the specific gravity of the electrolyte gives a fairly good indication of the state of charge of the battery. However, in a VRLA battery, it is not possible to measure the specific gravity of the electrolyte since it is completely absorbed in the spun glass micro porous separator. The terminal voltage of the battery is directly related to the concentration of the electrolyte. Therefore, if one were to measure the open circuit voltage of the battery, the state of charge can be determined. The Open Circuit Voltage (OCV) readings should be taken 24 hrs. after charging is discontinued. The OCV value is co-related to the state of charge of VRLA batteries as per the table enclosed. Sometimes, it may not possible to disconnect the batteries from service for 24 hrs. And then check the OCVs. Then the pattern of charging current delivered by a temperature compensated voltage – regulated charger after a discharge provides the alternate method for determining the full state of charge. The temperature compensation factor is –3 mV per cell oC rise from ambient temperature of 27oC.

Under normal conditions the batteries are floated at around 2.25 volts per cell, i.e. in a DOT system 24 cells are floated at 53.5 volts. During charging as the cells approach full charge, the battery voltage rises to approach the charger output voltage, i.e. 53.5 volts and the charging current decreases to the float current value ofaround 50 mA/100 AH for VRLA batteries. So, when the charging current has stabilised at the float current for three consecutive hours or the voltage across the battery bank terminals is constant for six consecutive hours, then the battery bank can be considered as having reached full state of charge.

If the charging voltage has been set at a value higher (but equal to or less than 2.30 VPC) than normal float voltage (so as to reduce charging time), it is normal practice to reduce the charging voltage to the float value of 2.25V after 12 hrs. Then the float current will soon stabilize and the above methods can be adopted for determining the state of charge.

Table

% State of Charge Open Circuit Voltage100 2.1590 2.1380 2.1170 2.0960 2.0750 2.0540 2.0330 2.0120 1.970 1.95

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CHAPTER-5Operation and Maintenance of SMPS Power Plant

1.1 WORKING PRINCIPLE OF SMPS POWER PLANT:What is SMPS?SMPS means Switch Mode Power Supply. This is used for D.C-to-D.C conversion. This works on the principle of switching regulation. The SMPS system is highly reliable, efficient, noiseless and compact because the switching is done at very high rate in the order of several KHz to MHz.NecessityThe SMPS regulators are used in B.S.N.L at various locations like CDOT, E10BTransmission systems etc.1.2 Principle of Switching Regulator:

]

A pulse train drives the base of ‘switching or pass transistor’. When the voltage to theBase is high, the transistor saturates, when the voltage is low, the transistor turns off. Here theTransistor functions as a switch. When the transistor is ON, load current is drawn through theTransistor and choke L. When the transistor is OFF the load current is maintained by theEnergy stored in the choke L. The current flows through earth, Diode D, choke, load andEarth. Hence this diode is called ‘Retrieval Diode’.Duty cycle of the Transistor = On Time = DOn Time + Off Time(One cycle time)The output voltage = Input voltage x D

For exampleIf I/P voltage is 200 volts and D=0.25O/P voltage = 200 x 0.25 = 50V.Regulation is achieved by modifying the Duty cycle. Duty cycle depends on onetimeof transistor, which in turn depends on the width of the pulse applied to the base of theTransistor, which is controlled by ‘Pulse width modulation’ by regulator circuit.1.2.1 Principle of Regulation:

The relaxation oscillator produces a square wave. The square wave is integrated to get a triangular wave, which drives the non-inverting input of a triangular to pulse converter. ThePulse train out of this circuit then drives the Pass Transistor. The output is sampled by aVoltage divider and fed to a comparator. The feed back voltage is compared with a referenceVoltage. The output of the comparator then drives the input of the triangular to pulse converter. If the output voltage tries to increase the comparator produces a higher output voltage, which raises the reference voltage of the triangular- to pulse converter. This makes the pulse that drives the base of the switching transistor narrower. That means duty cycle is reduced. Since the duty cycle is lower the output becomes less, which tries to cancel almost all the original increase in output voltage. Conversely, if the regulated output voltage tries to decrease, the output of the comparator decreases the reference voltage of the triangular -to pulse converter. This makes the pulse wider and the transistor conducts for larger time and more voltage comes out of the L.C.filter. This cancels out the original decrease in output voltage.

For maximum efficiency the duty cycle should be less than 0.5. As long as the triangular voltage exceeds the reference voltage, the output is high. Since Vref is adjustable,we can vary the width of the output pulse and hence the duty cycle. Switching regulators are more efficient than conventional regulators as the power loss in the switching element is reduced to minimum as it conducts only for a fraction of a cycle. Now a days SMPS technology is extended to power plants also. Power plants upto 2000A capacity have been developed using SMPS principle.

1.3 Specification of SMPS Power Plant:

1) Input Voltage 320 V to 480 VFrequency 45 Hz TO 65 Hz2) Output Voltagein Float Mode -54.0 ± 0.5 V. adj range -48 V to -56Vin charge mode : -55.2 V ± 0.5V3) Input power factor >0.95 Lag with 25% to 100% load at nominal input.

1.4 50V – 2000A POWER PLANT (Multi Rack Type): Suitable for VRLA Batteries with 100A SMPS Rectifier Modules

1.4.1 Introduction:The power system is intended primarily to provide uninterrupted DC power Telecom equipments and current for charging the batteries in the presence of AC Mains. The system works from commercial AC mains which is rectified and regulated to –50V DC and is fed to the equipment (exchange). The system has provision to connect three sets of VRLA batteries and facility to charge them simultaneously to ensure that uninterrupted DC power supply is always available to the exchange.The power system –50V, 2000A has the following features:(a) Multi-rack configuration.(b) Facility to parallel a maximum of 21 nos. (or 22 nos.) of 100A (5600W)Rectifier modules operation from three phases, 400V, 50Hz AC input.(c) Termination for three sets of VRLA batteries and exchange.(d) System input : Three phase, 4-wire, 50 Hz supply.The power system as a single DC bus called auto float/charge bus. Depending uponthe status of the batteries, the output DC voltage is maintained at 54.0 + 0.5 V under autoFloat condition. During auto charge the maximum DC voltage reached across the bus is 55.2

Volts. The exchange battery and rectifier modules are connected in parallel.The system employ natural convection cooling and has AC input distribution, DCOutput distribution, protection and alarm circuitry for rectifiers, battery and equipment.

1.4.2 Technical Specification For Module(1) Input Voltage:(a) 320V to 480V r m s three phase (Nominal Voltage – 400V).(b) Frequency: 45 Hz. 65 Hz.(2) Output Voltage:Float mode:Nominal voltage: -54.0 + 0.5V,Adjustment range: -48.0 to –56.0 VCharge mode Voltage: -55.2 + 0.5 V(3) Rated current: 100 Amps.(4) Psophometric noise :Less than 4 mV without battery floated.Less than 2 mV with battery floated.(5) Input power factor: Greater than 0.95 lag with 25% to 100% load at nominal input.(6) Efficiency :Greater than 90% at full Load and nominal input.(7) Protection:(a) Short circuit protection.(b) Input over/under voltage protection.(c) Output over voltage protection.(d) Constant current features settable from 80 Amps. To 110 Amps. In auto float/charge mode.(8) Alarms and indicating lamps :(a) FR/BC on Auto Float/Charge: Green LED(b) Rectifier module over voltage: Red LED(c) DC output fail/Under voltage: Red LED(d) FR/BC Over Load (Voltage Drop): Amber/Yellow LED(e) Mains Available: Green LEDFor System(1) Input Voltage :(a) 3 Phase, 4 Wire, 50 Hz (Range – 320V to 480V RMS)(b) Frequency: 45 Hz. 65 Hz.(2) Output Voltage:Float mode Voltage: -54.0 + 0.5VCharge mode Voltage: -55.2 + 0.5V(3) Rated Current:Equipment: 1100 Amps.Batteries: 300 Amps. Each(4) Protection(a) Short circuit/Over load protection.(b) Input over/under voltage protection.

(c) Battery/Equipment over voltage protection.

(5) Alarms and indicating lamps:(a) Load Voltage High - Red LED(b) Load Voltage Low - Red LED(c) Fuse Fail - Red LED(d) FR/BC Fail - Red LED(FR/BC No Output MCB Trip)(e) Mains available - Green LED(f) Mains out of range - Red LED(g) Mains Fail - Red LED(h) System (Exchange) Overload - Red LED(i) FR/BC Float/Charge Mode - Green LED(j) Mains “ON”/Battery Discharge - Red LED

1.4.3 Functional description of power system:This Power System is of multi rack type and consists of the following:(a) Eight racks – One main, one auxiliary and six extension racks.(b) AC Distribution module in each rack.(c) Rectifier modules (A maximum of three modules in extension rack and two each in main rack and auxiliary rack).(d) DC distribution module in each rack.(e) Metering in each rack.(f) Power system controller in main rack.(a) Rack:The rack is made of mild steel profiles with hinged front door. The door accommodates display and alarm enunciator. The rack is convection cooled and has Ventilator slots in the front and sides. The rear panel is screw type and can be dismantled. The cabinet accommodates 19” subsystems. Air baffles are provided for better heat transfer. Depending upon the load requirement (Equipment and Batteries), additional modules can be added. The bottom and top also have ventilator features. The DC power termination and distribution is done at the top. The AC power termination and distribution is done at the bottom.

(b) AC Distribution Panel:The AC input to the rack is terminated at the bottom of the rack on screw typeTerminals. Individual AC circuit breakers are provided for each module. The line, neutral andEarthing cabinet are terminated on moulded plug which is fixed to the respective sockets onThe rectifier module. To monitor AC input current, 3 nos. of single phase AC currentTransformers are mounted on the panel of main rack. A small signal transformer is mountedOn the PSC panel to provide AC input to power system controller card.

(c) Rectifier module:The SMPS rectifier module – 50V, 5600 watts works on 400V AC input and provides – 50V DC for system. The input is through 9-pin AC socket and the DC output is through terminals. The module has front panel to indicate status and faults in the module. The control signal is taken through 8-pin telephone jack and is terminated on to the power system controller card. The

rectifier modules are convection cooled and can be jacked in and out of the cabinet easily. The DC output from each module is terminated on the respective DC bus bar mounted on the DC distribution panel.

(d) DC Distribution Panel :This panel is mounted at the top of the cabinet. The panel incorporates the following :(1) Input from individual rectifier modules terminated on cabinet.(2) DC shunts to monitor current in various paths.(3) Termination of battery 1, 2 and 3.(4) Termination of equipment positive and negative.(5) Fuses for battery 1, 2 and 3.

(e) Metering:The front panel of main rack consists of two AC meters to monitor individual line toLine voltage and current. The selector switch selects the relevant phases. The DC metersMonitor both voltage and current of batteries and exchange.

(f) Power system controller:The Power system controller card consists of an electronic circuit which monitors theState of each rectifier module and display their status. It also controls the operation of theModule so as to make it work in auto float or auto charge mode. The current signals areMonitored continuously to ensure equal sharing of current. In case of faults, the same isDisplayed and for faults like input voltage beyond limits, DC output over voltage, over loadEtc. it shuts off the module. The various alarms as per following details are displayed on theFront panel with audible alarm.(1) Mains out of range: Red(2) Load voltage high (above 57V) : Red(3) Load Voltage low (below 42V) : Red(4) Mains fail: Red(5) System overload: Red(6) Mains available: Green(7) System over load: Red(8) Mains on battery discharge: Red(9) FR/BC in Float-charge mode: Green (5) System overload: Red(6) Mains available: Green(7) System over load: Red(8) Mains on battery discharge : Red(9) FR/BC in Float-charge mode: Green(10) FR/BC Fail: Red

1.4.4 Functional Description of Rectifier:The SMPS 50V-5600W rectifier is a state-of-the-art switch-mode power conversion equipment. The unit consists of two cascaded power converters performing power factor correction and DC/DC conversion. The power stages are synchronized and working with constant switching frequency of 100 kHz. The rectified AC mains voltage is processed first in the power factor

corrector circuit, which is based on a boost topology. The boost converter has the inherent advantage of continuous input current waveform, which relaxes the input filter requirements. The performance of the basic boost cell is improved by a proprietary snubber circuit, which reduces the switching losses of the power semiconductors due to non-zero switching times. Furthermore, the snubber circuit also decreases the electromagnetic interference (EMI) generated primarily during the turn-off process of the boost diode. The output of the boost converter is a stabilized 400V DC voltage. Further conversion of the stabilized high voltage output of the power factor corrector circuit is necessary to generate the isolated low voltage output and to provide the required protection functions for telecommunication application. These tasks are achieved in the DC/DC converter circuit, which is based on a full-bridge topology. The full-bridge circuit is operated by phase-shift pulse with modulation with current mode control. This control method provides zero voltage switching condition for all primary side power semiconductors effectively reducing switching losses and electromagnetic interference. An advanced solution reduces the stresses of the output rectifier diodes. Proper operation of the power converters is managed by individual controller circuits and supervised by the housekeeping electronics. Remote commanding and monitoring of the modules are possible through a power system controller housed in the system.

1.4.5 Functional Description of Power System Controller:

Power system controller is designed to control the modes of operation of rectifiers,Acknowledge and displays the status of rectifiers and system and controls parameters ofRectifiers. The controller accepts signal from individual rectifiers through 8-pin telephone jackAnd controls the operation of each individual rectifiers. The mode of operation of rectifier modules depends on the coded signal M1 and M2 from the controller. Depending on the state of batteries, the ATM circuit either gives a signal for floats or charge. An encoder to obtain suitable coded signals encodes these signals M1 and M2.

Depending upon the mode of operation of Rectifier modules, they acknowledge codedSignals S1 and S2. These signals are decoded to display whether the modules are in autoFloat /charge or fail condition. The total battery current can be suitably programmed to limit the current supplied from the modules through current programming pin in modules.1.5 SMPS 48V – 5600W 1.5.1 Introduction

The SMPS 48V-5600W is a three-phase, unity power factor power supply with a wide Input voltage range of 3 X 185 Vac to 275 Vac (with neutral wire) and with a useful output Power of 5600W delivered to the load. This unit has been developed for cost effective but Highly intelligent modular telecommunication power systems. It fulfills the specification of TELECOMMUNICATION ENGINEERING CENTRE (DOT) for the S.M.P.S. BASEDPOWER PLANT GENERIC REQUIREMENTS (No. G7SMP/-01/01 JULY 04) Primary application of the rectifiers SMPS 48V-5600W are in the supply of Telecom equipment. The convection cooled unit may be operated up to 60oC ambient air temperature.The rectifier operates from a nominal 3 X 230 Vac rms (with neutral wire) source. The mains frequency may vary from 45 Hz to 65 Hz. Total harmonic distortion (THD) of the input current wave form is below 5%. The output of the rectifier conforms to the generic requirements of

telecommunication power supplies in terms of noise, voltage programmability, as well as over voltage, overloaded short-circuit protection. The rectifier SMPS 48V-5600W can be set in the 3 modes ‘auto float’, ‘auto charge’ and ‘manual boost’ by the power system controller.1.5.2 General description of operationThe SMPS 48V-5600W rectifier is a state-of-the-art switch-mode power supply. It is Composed of 3 identical single-phase sub-modules (R, S and T) as shown in the block Diagram .The sub-modules are connected between neutral and one of the phases (R, S or T) on the input , and in parallel on the output. All ‘-‘ wires are protected by circuit breakers, which are mechanically coupled.

The interface card IFC 52 provides:1. All reference voltages and protections to the sub-modules.2. Signalization and manual interface (adjustment potentiometers and test jacks)For the whole unit, and3. Communication with power system controller ‘ITI’.Each of the sub-modules consists of two cascaded power converters performing over factor correction and dc/dc conversion. The power stages are synchronized and working with constant switching frequency of ~100 kHz. The rectified ac mains voltage is processed first in the power factor corrector circuit, which is based on a boost topology. The boost converter has the inherent advantage of continuous input current waveform, which relaxes the input filter requirements. A proprietary snubber improves the performance of the basic boost cell circuit, which reduces the switching losses of the power semiconductors due to non-zero switching times. Furthermore, the snubber circuit also decreases the electromagnetic interference generated primarily during the turn-off process of the boost diode. The output of boost converter is a stabilized 400 Vdc voltage. Further conversion of the stabilized high voltage output of the power factor corrector circuit is

necessary to generate the isolated low voltage output and to provide the required protection functions for telecommunication application. These tasks are achieved in the dc/dc converter circuit, which is based on a full-bridge topology. The full-bridge circuit is operated by phase-shift pulse-width modulation with current-mode control. This control method provides zero voltage switching conditions for all primary side power semiconductors effectively reducing switching losses and electromagnetic interference. An advanced solution reduces the stresses on the output rectifier diodes. Proper operation of the power converters is managed by individual control circuits and supervised by the housekeeping electronics. Remote commanding and monitoring of the modules are possible through a power system controller.

1.5.3 Block diagram of a single sub-module R, S or T:This chapter gives more detailed information about the technical merit of single sub

module based on the functional blocks shown in the diagram below (R, S and T).

Block 1 of the drawing presented above is the input EMI filter of the rectifier. The Fixed frequency, synchronized operation of the different circuits allowed to optimize the Filter’s performance. It has only one differential and one common mode filter stage. Block 2 represents the Inrush Current Limiter circuit, which consists of series combination of surge rated power resistors and fuse. The circuit limits the input current of the rectifier during the initial charging of the energy storage capacitors connected to the output of the boost power factor corrector circuit. In normal operation the current limiting components are by-passed through relay, which is controlled by the housekeeping electronics.A general purpose full-wave Bridge Rectifier circuit forms Block 3. It is directlyMounted on the heat sink.

1.5.4 Power factor corrector:

The power stage of the Power Factor Corrector is a boost converter represented by Block 4. The circuit operates with 100 kHz constant frequencies in continuous inductor current Mode. Because of the relatively high switching frequency a loss-less snubber has been added to

the basic boost converter to reduce switching losses and semiconductor stresses. When the boost transistor conducts the energy being stored in the boost inductor increases. During the off state of the transistor energy is transferred from the inductor to the output capacitor through the boost diode. The inductor current is measured with a sense resistor and it is forced to follow the input voltage waveform. The technical literature refers to this technique as the resistor emulation mode, which is the most preferred load by the utility companies. Number 5 in the block diagram marks the output Capacitor of the boost converter. This capacitor is used for low-frequency energy storage as well. Due to the nature of ac sources the energy absorbed at the input of the unit varies according to the mains cycle. In order to deliver constant power at the output energy must be stored inside the unit. Therefore, high voltage 450V electrolytic capacitors are used at the output of the boost converter to provide cost and volume effective energy storage. Block 12 is the controller of the Power Factor Corrector. It uses the UC3854B integrated circuit that had been developed to control boost converters in power factor corrector applications. This integrated solution takes care about all sensing, controlling and protection functions which are necessary to achieve proper input current waveform and to stabilize the output voltage of the power factor corrector circuit. The control principle implemented in the UC3854B is average current mode control.

1.5.5DC/DC Converter:The heart of the module is the dc/dc Converter shown in Blocks 6-9. Block 6 shows the primary arrangement of the full-bridge power converter employing a safety isolated high frequency transformer. Because of its important role in providing safety isolation between the Input and the output of the module, the transformer coupling is emphasized in Block 7. The Secondary side of the dc/dc stage provides rectification (Block 8) and filtering (Block 9) Functions, which are realized using current-doublers topology. Particularity of the implemented Solution is integration of two inductors on a common ferrite core. The full-bridge converter takes energy from its input when two diagonally located switches are turned on at the same time. This energy is transferred to the output through the transformer immediately. The energy will be stored in the output filter inductor showed in Block 9 and transferred to the output capacitor of the dc/dc converter during the passive interval when energy is not absorbed from the source. This sequence can be achieved by different ways depending on the implemented control strategy.

The dc/dc Controller, shown in Block 13, is using the phase-shift pulse width modulation technique that provides loss-less, zero voltage turn-on condition for the primary side semiconductors. Further benefit is the greatly reduced electromagnetic interference generated by the converter. The control principle is peak current mode control. Like the power stage, the controller circuit of the dc/dc converter is also divided between the primary and the secondary side of the rectifier. Communication between the separated parts is realized using optical isolators marked by number 14.Major part of the dc/dc controller is referred to as Secondary Controller in Block 15. The secondary side controller is responsible for output voltage and current regulation Functions.

1.5.6 Output Section:Block 10 forms the physical Output Section of the sub-module. It is a shielded, Common-mode, low-pass filter stage to reduce conducted electromagnetic interferences to theRequired level.

1.5.7 Housekeeping:The name Housekeeping refers to the auxiliary power supply and to all internal Primary side supervisory functions necessary for the operation of the unit. Besides the Auxiliary power converter (current-mode controlled fly-back converter), Block 11 also Includes the master clock, under- and over-voltage lock-out, and start-up sequence generator.

1.6 Output Characteristics:The power system controller can set the rectifier into the 3 modes of operation, i.e. ‘auto float’, ‘auto charge’ and ‘manual boost’. The output characteristic is different for these 3 modes as shown below :‘auto float’

‘auto charge’ mode

1.7 INSTALLATION & MAINTENANCE OF SMPS:

The power system installation is simple please do the following step by step.• Unpack all the boxes. Check for physical damages. Compare the contents with the packing list.

• put the main rack at the desired place then, the auxiliary rack in the left side of the main rack. And then grow the extension racks in the extreme left.

• Connect the joining bus bars to link the main and the Auxiliary racks.

• put the 5600W rectifiers in their respective slots in each rack. Any rectifier modules can be put in any slot.

• Connect each ac input cable (White cable with nine pin male connector) to the respective female socket provided in the right side in each module.

• Connect each pair of DC output cable (Red & blue cable) in the respective terminal blockProvided in the left side in each module. PLEASE ENSURE THAT THE RED CABLE IS

CONNECTED TO THE TERMINAL MARKED AS ‘+’ (RED TERMINAL BLOCK) ANDBLUE CABLE TO THE TERMINAL AS ‘-‘ (BLUE TERMINAL BLOCK).

• 02 nos. of eight pin flat cable connectors are provided for each rectifier module (except the lastModule, where only one connector is provided). Connect these on the sockets provided on eachModule so that control bus is connected in daisy chain. Finally check that the common system bus is extended to the connector JP3 of the PSC card. Ensure that there is no break in the daisyChaining of control bus.

• Connect three-phase four wire input to each rack at TB1. Input points are marked as R, Y, B, NJust below the terminal block TB1. Also the terminal blocks are provided with red, yellow andBlue markers. PLEASE ENSURE THAT THE NEUTRAL IS CONNECTED TO THETERMINAL MARKED AS “N” (HAVING NO MARKER).

• Ensure that all the AC side MCBs (mounted on AC distribution panel) as well DC side MCBs,(Mounted on DC distribution panel) are in OFF condition.

• Switch on the AC input. Check the availability of AC voltage on the front panel of the power plant for each phase. If the AC I / P is within the range (320-480 volt) switch on the MCCBs in the sequence given in the Table-1 and do the NO load test for each module.

1.8 NO LOAD TEST:

No Load test: First ensure that all AC side MCBs (mounted on AC distribution panel), as well as DC side MCCBs are in OFF condition. Switch ON the AC input. Check the availability of AC voltage on the front panel of the power plant for each phase. If the AC I/P is with in the range(320-480) switch on the MCBs in the following sequence.

MCBAC SIDE

MCBDC SIDE

Module energized

DC VM/AMSEL POSN.

DC output In all the 6Position of DC VM/AMSEL

Remarks

CB1 CBM1 M1 Posn.1– EqptPosn. 2 – BTY1Posn. 3 – BTY2Posn. 4 – BTY3Posn. 5 – BTY4Posn. 6-System

54.0 ± 0.5 v If every thing is OKisolate the moduleM1 by switching offthe breakers CB1 &CBM1.

CB2 CBM2 M2 -do- -do If every thing is OKIsolate the moduleM2 by switching offThe breakers CB2 &CBM2.

CB3 CBM3 M3 -do- - do- If every thing is OKIsolate the moduleM3 by switching offThe breakers CB3 &

After each module has been energized separately at no load, switch ON all the MCBs and check that DC out put remains within 54.0±0.5V in all the five positions of DC VM SEL.

1.9 Load Test:- Load Test of the unit has to be done with suitably rated resistive loads as per Table-.

LOAD TEST TABLE-2

MCB ACSIDE

MCB DCSIDE

Module Energy

SEL

DC VM/AM In all the 6 Posin of VM POSN.

DC output pathsSEL

Resistive load in different

Remarks

CB1 CBM1 M1 Posn. 1– EqptPosn. 2– BTY1Posn. 3– BTY2Posn. 4– BTY3Posn. 5– BTY4Posn.- 6 System

Auto floatVoltage –54.0 ± 0.5 v

Auto chargeVoltage –55.2 ± 0.5 v

Eqpt. Path-increase thecurrent slowly from 0 to105 A. The voltage droopPhenomena will start at theFactory set currentLimit (somewhere between100 to 105 A)BTY1- No loadBTY2- No loadBTY3- No loadBTY4- No load

BTY3 –increase the BTY3path current slowly from 0 to 100 A. The unit will go to Auto charge mode when current exceeds factory atLimit ( 1% of total AH capacity of both the batteries) for ex. In case of 4x2500 AH battery banksThese limit shall be 1000 A. Check that Auto float voltage and auto chargeVoltage are within the limits.

If every thing is OKIsolate the module M1 bySwitching off theBreakers CB1 & CBM1.

1.10 Repeat the same for CB2 & CB3:

After each module has been checked on full load of 100 Ampere, switch ON all MCBs, and load 300 Ampere in equipment path, 100 Amp. In each battery path, and see that the rack voltage remains at 55.2 ± 0.5 volt for 600 A system.

1.11 BATTERY PATH CURRENT LIMIT PROGRAMMING:

Pot R86 in the PSC card is used to set the current limit in the battery path. For the 2200Amp power system there is a provision of 4x2500AH batteries and for these batteries, the factory set values of the current limit is 10000A (i.e., 10% of the total AH capacity of the batteries). However if the user wants to change this value then the POT R86 needs to be varied carefully to set the current limit at the desired value. For example, suppose initially the installed capacity is 3x2500 AH and accordingly the battery path current limit may be set at 750 A. For these when the battery path draws more then 750 A, vary the pot slowly in one direction and stop when the bus voltage droops and battery path current becomes 750 A. In these case, overload lamp (yellow LED ) shall be lighted on all the modules. If the voltage does not droop even when the pot has reached it’s extreme end, then vary the pot in other direction and stop as soon as the bus voltage droops and battery path current becomes 750 A. In these case, overload lamp ( yellow LED ) shall be lighted on all the modules.

1.12 SURGE ARRESTER ASSEMBLY:

Four numbers of surge arrestors has been installed directly across A.C. input terminals in the main rack of the system to protect the rectifier modules (contained in all the racks) in the system from high energy content surges caused by lightning or sudden switching OFF, off heavy inductive loads. The surge arrestors contains two parts- plug and socket. In case of surge arrestors going faulty, there shall be an indication on the front of the plug. In such case the plug need to be replaced.

1.12 Dimensioning of the bus-bars/cables for load & battery path with respect to the ultimate capacity of SMPS power plants:(As per the specifications of TEC, the following calculations may be followed)The basis for calculation;1, The Ultimate Load: x2. Redundancy: 10% of Ultimate load (0.1 *x).3. Battery-back-up: 6 hours4. Battery capacity: 6 hour back-up up to 80% DOD (near available capacity)5. Safety factor: 25% of the load.6. Power plant Ultimate capacity: CCalculations:Load; xRedundancy: O.l xBattery capacity: 6x/0.8 = 7.5xBattery Charging Current @ Cio = 7.5x /10 = 0.75xPower plant Ultimate Capacity: C= (x + 0.1x + 0.75x) = 1.85xTherefore x = C/1.85Safety factor for bus-bar/cable : 1.25The bus-bar/cable shall be rated = 1.25*x = 1.25* (C / 1.85) = 0.68*CSo the bus bar / cable chosen for load path shall be capable to handle the 70%of the ultimate capacity of the power plant. As there may be an eventuality when only one battery is connected to the load, the size of bus-bar in each battery path shall also be the same. The size of the bus-bar/cable for load & each battery path shall be higher than 70% of the power plant ultimate capacity. However the common bus-bar/cable used for connecting the FR/FCs to the input of the distribution unit shall be the rating for the ultimate system capacity.

1.13 MAINTENANCE SPARES FOR POWER PLANT:As the power plant plays an important role in any telecom system, it has to be maintained in Fault free condition when any unit goes fault, it is to be attended on topmost priority to restore the power system. Hence it is necessary to keep Fuses, PCBs etc as spare. These are called “Maintenance spares of power plant and are to be supplied along with power plant by the Manufacturer. As per TEC specification No. TP 120-M-91/TP-130-F-93/G PPL-01/03 FEB 93, the list of spares to be supplied by the manufacturer is given in Table I and II.TABLE-IList of spares to be supplied along with each unit of power plant (general)

I. FusesAC Input fuses 100%DC output fuses 100%Semiconductor device fuses 100%Smoothing condenser fuses 100%Auxiliary circuit fuses 100% (each type)Alarm type fuses 100% (each type)II. Fuse mounting assembly 1 No. Each type.II1.Semiconductor devicesDiode 50%Thyristor 50%Transistors 50%

IV. Surge suppression elements:Resistors 2 nos.Capacitors 2 nos.MOVs 2 nosV. Smoothing condenser 2 nosVI. Auxiliary transformer 1 no. Each typeVII Glass epoxy PCB assembly completeWith component with card extender. 1 no. Each typeVIII. Control circuit componentsDiodes 2 nos each typeSCRs -do-ICs -do-Transistors -do-Zener diodes -do-UJTS -do-Pulse transformer -do-Lamp/LEDs/mains ind lamps -do-TABLE-2List of spares to be supplied along with each set.Description Qty Rating100A 200A 400A 600AFusesAC Input fuses 3 TIA20 TIS36 VSB63 VSB100DC Output fuses 1 VSB125 VSF200 VSK400 VST630

Smoothing condenser fuses: 2 TIA25 TIA25 TIS63 TIS63Auxiliary Circuit fuses 2 NS4 NS4 NS4 NS4Alarm type fuses 7 3.0A 3.0A 3.0A 3.0AFuse mounting 1 20 A 20 A 20 A 20 ASemiconductor device thyristor 3 71RIA4

Surge Suppression elements:Resistors 2 10 . 1 WattCapacitors 2 0.22 mfd 250VSmoothing condenser 2 10,000 mfd 100VAuxiliary transformer 1 0.415V/0.22, 0.22VGlass epoxy PCB assembly complete with component with card extender1 3-phase angle control card (30-3-0712/R1)1 Power supply +Amplifier card (30-3-0672/R21 SCR Trigger card (30-3-0672/R2)1 Supervisory card (12-92-01)1 Sequential switching card (12-92-05)1 Current sharing card (12-92-04)Control circuit componentsDiode 2 IN 4007SCR 2 SN 104 BOICs 2 741/2 4050/2 555

Transistors 2 CL 100/2 2N 3501/2 2N 2222Zener Diodes 2 5.6V/2 13.0VPulse Transformer 2 4503LEDs 2 5mm RedMain Indicting LEDs 2 10mm Red2 10mm Yellow2 10mm Green

1.14 SAFETY NOTICE:Before applying power to the system, please ensure that the body of the cabinet is properly earthed if the earthing is not proper, the surge protection set installed in the system /at the site may not work & the consequential damage to the SMPS modules because of this shall not be governed by the warranty clause. Before taking the insulation test of the rack, isolate the SMPS modules & remove the surge arrestor plug from it’s base. 1.15 WARNING• Hazardous voltages of 415 V rms will be present when a AC input power is energized.Qualified personnel must use extreme caution when operating & maintaining the system.• Initial battery connection & exchange connection shall be done without energizing theSystem. When the system is under operation adequate precaution has to be taken whileInstalling & removing SMPS modules since high voltages (400V AC) are available on theFront panel.• Please ensure that there is no ceiling fan over the power system racks, as this disturbs theNatural convention cooling of the racks.